1. Field of the Invention
The present invention relates to an exhaust gas cleaning apparatus for an engine, such as a diesel engine, that uses a particulate filter to collect and remove particulate matter from the exhaust gas discharged from the engine. Additionally, the present invention relates to a method of determining the particulate matter accumulation state of the particulate filter.
2. Background Information
Harmful exhaust components such as carbon particles and other particulate matters (particulate matter or “PM”) contained in an exhaust gas have become an enormous problem especially in diesel engines. Conventionally, various types of particulate matter capturing filters (Diesel Particulate Filter or “DPF”) have been used as exhaust gas after-treatment devices to collect and remove the particulate matter contained in the exhaust gas.
When this type of particulate filter is used, the particulate filter needs to be regenerated when an amount of accumulated particulate matter reaches a prescribed amount by combusting the particulate matter accumulated in the particulate filter. Therefore, it is necessary to determine or estimate an amount or degree of the particulate matter accumulated in the particulate filter.
Japanese Laid-Open Patent Publication No. 3-233126 describes an exhaust gas cleaning apparatus in which an air fuel ratio of an exhaust gas discharged from an engine is detected and an amount of particulate matter accumulated in a particulate filter within a prescribed time unit is calculated based on the air fuel ratio of the exhaust gas. Then, the amount of particulate matter accumulated within the prescribed time unit is consecutively integrated (added up) over time to determine to regenerate the particulate filter when a value of the integration calculation reaches a prescribed value. Moreover, the exhaust gas cleaning apparatus described in the above mentioned reference is configured such that a mandatory regeneration is executed for a prescribed amount of time and then the regeneration stops. When the regeneration stops, the amount of accumulated particulate matter calculated is reset to 0.
In view of the above, it will be apparent to those skilled in the art from this disclosure that there exists a need for an improved exhaust gas cleaning system. This invention addresses this need in the art as well as other needs, which will become apparent to those skilled in the art from this disclosure.